In the field of gas chromatography, one of the critical areas where events leading to analytic errors can occur is at the interface between the chromatographic column and the sample injector. There are several events surrounding the injection of sample which can lead to sample loss or less than ideal sample injection.
Gas chromatography of the type to which the invention pertains generally comprise a pyrolysis/volatilization chamber in which the sample is pyrolyzed or otherwise volatilized before being conducted onto the chromatographic column.
One such type of gas chromatograph are those used in the field of pyrolysis (Py)-gas chromatography (GC), particularly high resolution gas chromatography (HRGC), and Py-GC-mass spectrometry (MS). An example of the use of Py-GC-MS is described for instance in Holzer, et al., Analysis of In Situ Methylated Microbial Fatty Acid Constituents By Curie-Point Pyrolysis-Gas Chromatography-Mass Spectrometry, J. of Chrom., vol. 48, pp. 181-190 (1989), hereby incorporated herein by reference. This technique has developed into a widely accepted technique which is particularly powerful in the analysis of non-volatile materials, such as high molecular weight organic compounds, synthetic polymers and complex biological materials. Thermal degradation of these substances generate a large variety of decomposition products, which range from chemically related isomers to compounds that differ in polarity, structure and molecular mass. The diverse chemical nature of the decomposition products demands rigid standards for the analytical system. Furthermore, the samples to which this technique is applied are often very small, putting the preservation of sample and efficient and concentrated sample introduction onto the column at a premium.
With respect to the preservation of sample, small quantities of sample usually must be placed on a heating element, such as a resistive filament type pyrolyzer, or ferromagnetic Curie-point pyrolyzer probe, and introduced into the environmentally isolated pyrolysis/ volatilization chamber. This process is difficult because the filament/probe must be inserted through a septum (used to protect the column environment) which can disturb the sample, causing sample loss or spreading of the sample over the surface of the filament/probe which can disturb he uniformity of presentation of the volatile products to the chromatographic column.
Another problem in the injection of volatilized material onto a chromatographic column is the difficulty in maintaining the uniform concentration of volatilized analyte supplied to the column. One factor pertaining to this problem is the condensation of volatilized analyte upstream of the chromatographic column. Some injector systems actually are designed to facilitate such condensation through the use of an inert support material in the path of the volatilized sample products. Condensation of the volatilized sample products can diminish the amount of material actually reaching the column, as well as generally disrupting the regularity of flow of analyte to the column and even possibly rendering the mixture of the volatilized sample products reaching the column non-uniform with respect to product mix. Therefore it is desirable to produce an injector which efficiently and uniformly supplies volatilized sample products to the chromatographic column.
Pyrolytic reproducibility and the minimization of secondary reactions, to optimize resolution through rapid sample introduction, are also desirable characteristics in GC and GC-MS systems.
As mentioned above, chromatographic columns are often used in conjunction with a detector and/or a mass spectrometer. In calibrating such systems, pure samples are often injected. In such cases, is desirable to be able to efficiently throughput amounts of pure sample from a chromatographic column. In the case of mass spectrometers, calibration normally must be carried out by use of a direct insertion probe (DIP). To use the DIP, a second, auxilliary inlet must be used to insert the DIP inserted into the vacuum chamber of the mass spectrometer. This insertion poses a risk that the vacuum of the instrument might be broken and the spectrometer contaminated. Accordingly, it is also desirable to be able to produce a GC-MS system capable of operating in both a classical GC-MS analytical mode and a rapid pure sample through mode, without the need to disassemble the GC-MS and risk contamination or damage to the instrument.
The general function of a high pressure (HP) split/splitless injector or any other model split/splitless injector is to deliver a small volume (several nanoliters) onto a high resolution capillary column. This small volume is necessary to avoid overloading high resolution capillary columns with sample capacities in the range of 10-75 nanograms.
Unfortunately, the lower limit on syringe volume is in the microliter range (1000 nanoliters) so the sample must be reduced in volume to introduce it onto the column in a narrow band which is very important in high resolution GC. This is accomplished by splitting the sample in a ratio of 1:100 or 1:10000 where the first number is the amount introduced onto the column and the second number is the amount vented to the atmosphere by the split injector. As pointed out above, one disadvantage of this technique is loss of sample which may only be present in trace amounts. Another major disadvantage is that quite often the composition of the split sample does not reflect the actual composition of the original sample thereby making quantitative work difficult. This is especially true when the components of the sample encompass a wide range of boiling points.
The splitless mode of injectors allows for entire sample introduction onto the column. However, it is often difficult to place a sample onto a column when a relatively large amount of solvent accompanies the analyte as is typically the case. The first technique commonly used to separate the solvent is known as cold trapping. This method typically requires recondensation of the sample at the beginning of the column. The sample will be introduced much more slowly onto the column but will not spread out very far due to the fact that the liquid will become immobilized and the volume of the liquid is much less than the volume of the gas. Recondensation is accomplished by keeping the temperature twenty degrees below the boiling point of the least volatile component. The temperature is slowly raised to volatilize the compounds trapped at the beginning of the column.
Another technique used to deal with this large amounts of solvent is the use of the solvent effect method. In this method the solvent is recondensed at the beginning of the column and the analyte is introduced and dissolves into the liquid solvent. The temperature is then slowly raised to allow the sample components to elute off the column. Both of these techniques are used to when sample volumes larger then the capacity of the column are injected.
Accordingly, it is desirable to be able produce an injector which is capable of introducing a sample onto a chromatographic column without recondensation of the sample by cold trapping, or the use of solvent effect recondensation.
Of course, such solvent-based injection techniques are only applicable to the injection of solvated analytes. Thus, it is also desirable to be able to produce an injector capable of injecting samples where it is impossible or undesirable to use solvent, such as in the case of insoluble samples or samples in very small quantities.
The present invention is most applicable to the fields of biochemistry, biotechnology, food science, forensic science and environmental monitoring.
In view of the disclosure of the present invention and from the practice thereof, additional advantages and the solution to other problems may become apparent to one of ordinary skill in the art.